The present invention generally relates to refrigerated devices having cooled enclosures such as refrigerators and/or freezers. More specifically, the present invention relates to minimizing the maximum temperature that the cabinet temperature of an enclosed freezer will attain during defrost, thus increasing performance.
Commercial and domestic refrigerators and freezers are provided with a refrigeration unit for cooling. The refrigeration unit typically has a compressor driven by a compressor motor, a condenser and an evaporator. As the refrigeration unit operates, water vapor condenses on the evaporator and results in the build-up of frost and ice on the evaporator. The build-up of frost and ice on the evaporator results in diminished airflow through the evaporator and a reduction in the ability of the refrigeration unit to cool the air within the refrigerator or freezer. To enhance the efficiency of refrigerators and lower their power consumption, many refrigerators are designed to periodically defrost the evaporator. Defrost devices, such as heaters, are often used to hasten the defrost operation. Also known are refrigerators that defrost on demand by sensing an accumulation of ice and, in response, initiate a defrost operation.
However, the prior art refrigerators and freezers fail to teach a demand defrost scheme that uses temperature measurements that are directly related to heat transfer principles as a basis for determining condensate accumulation. Accordingly, the prior art refrigerators and freezers have inherent inefficiencies. The prior art refrigerators and freezers are also burdened with overly complex algorithms and timing considerations.
Generally, there are three known ways or techniques for controlling the operation of a compressor and a defrost heater with what is referred to herein as a defrost cycle controller. These three ways are referred to herein as real or straight time, cumulative time, and variable time.
The real time technique involves monitoring the connection of the system to line voltage. The interval between defrosts is then based on a fixed interval of real time.
The cumulative time method involves monitoring of the cumulative time a compressor is run during a cooling interval. The interval between defrost cycles is then varied based on the cumulative time the compressor is run.
The variable time method is the most recently adopted method and involves allowing for variable intervals between defrost cycles by monitoring both cumulative compressor run time as well as continuous compressor run time, and defrost length. The interval between defrost cycles then is based more closely on the need for defrosting.
As is known, during a defrost cycle there is also dripping of melted frost to a drip pan from which the melted frost evaporates. This is known as the drip mode or cycle.
The United States government, as well as other governments, has continuously enacted more and more stringent laws and regulations relating to the efficiency of refrigerators and freezers, particularly as home appliances. As a result, much research has been directed to more effective control over the refrigeration cycles of refrigerators and freezers and, particularly, to the defrost cycle, since in this cycle, the effect of refrigeration is, on the one hand, counteracted by removing cold from the enclosure, and on the other hand, enhanced by increasing the efficiency of refrigeration by removing insulating frost.
Furthermore, different types of frost control systems have been utilized, varying from the use of a timer to periodically initiate and terminate defrost to sophisticated infrared radiation and sensing means mounted on the fins of the refrigerant carrying coils.
Other such defrost systems generate a signal in response to an air pressure differential across the heat exchanger caused by frost accumulation blocking the airflow through the heat exchanger. Other defrost systems require coincidence between two independently operable variables each of which may indicate frost accumulation such as air pressure within the shroud of the evaporator and the temperature differential within the evaporator coil. Another system may be the combination of a periodic timer to initiate defrost with a thermostat for sensing refrigerant temperature to terminate defrost. Another defrost system is one wherein compressor current or another operational parameter is monitored and compared to a reference level signal generated during a non-frost condition such that a variation from that reference level of the parameter being monitored indicates that it is time-to-initiate the defrost cycle.
These defrost systems can generally be grouped into two specific categories: timed and demand. A timed system simply initiates defrost periodically whether frost has accumulated or not based on the knowledge that all heat pump systems will need periodic defrosting under certain weather conditions. The amount of time chosen for periodically initiating defrost is a compromise between a short time that would cause a waste of efficiency during weather conditions which do not necessitate defrost and a long time which would allow the heat pump to operate inefficiently with a severely frosted evaporator coil. The advantage of a timed defrost system is that the heat pump will be defrosted periodically. The disadvantage is that the needed time between defrosts is never quite the same as the preset time due to weather conditions which differ from day to day and from location to location.
Demand defrost systems attempt to initiate a defrost cycle as a function of some system parameter which is related to a measure of frost accumulation. The advantage of a demand defrost system is that the heat pump is allowed to continue normal operation without energy consuming defrost cycle until defrost is actually required. The disadvantage of demand defrost systems is that initial equipment cost is high and demand systems are less reliable in their ability to sense the need for defrost.
Accordingly, it is desirable to provide an improved automatic freezer defrost cycle that is independent of the normal cabinet temperature cycle.
It is therefore a feature and advantage of the present invention to provide an automatic freezer defrost cycle that is dependent on the normal cabinet temperature cycle by identifying cold excursions of the temperature cycle and initiating defrost at that point. Thus, the defrost cycle initiates at cooler temperatures within the normal temperature cycle and therefore exposes the interior of the freezer to warmer temperatures less frequently.
The above and other features and advantages are achieved through the use of a novel algorithm as herein disclosed. In accordance with one embodiment of the present invention, a method of automating freezer defrost cycles is disclosed. This method determines when the defrost cycle should begin and sets a flag which indicates a time for defrost when the low point in the temperature cycle is reached. Thus, initiating the defrost cycle at this low point in the temperature cycle results in minimizing the maximum temperature that the cabinet temperature of the enclosed freezer will attain during defrost, thus increasing performance.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.